Feature request: Generate file, overwrite if Terragrunt signature found, otherwise do nothing

[anlutro]

Currently there is the if_exists = "overwrite_terragrunt" option, which according to documentation "overwrites the existing file if it was generated by terragrunt; otherwise, error"

However, it would be nice to have another option which overwrites the existing file if it was generated by Terragrunt, otherwise do nothing, instead of erroring.

An example use case for me would be provider configuration - most of our Terraform configuration should run on the latest version of the provider, but there are exceptions which are affected by bugs, which we'd like to keep at an older version.

We can kind of have this working with if_exists = "skip", but it means we have to manually delete the generated file every time we want to upgrade the provider.

[brikis98]

An example use case for me would be provider configuration - most of our Terraform configuration should run on the latest version of the provider, but there are exceptions which are affected by bugs, which we'd like to keep at an older version.

Trying to understand the use case more... For these exceptions, are you manually creating a provider.tf file that's checked into version control... But normally, no such file exists... So you want Terragrunt to create (and overwrite?) the file if it was originally written by Terragrunt, but otherwise, do nothing?

[anlutro]

Given the exame given in the Terragrunt documentation:

generate "provider" {
  path      = "provider.tf"
  if_exists = "overwrite"
  contents = <<EOF
provider "aws" {
  region              = "us-east-1"
  version             = "= 2.3.1"
  allowed_account_ids = ["1234567890"]
}
EOF
}

This'll generate terraform.tf with a Terragrunt signature. If I change the "contents" variable by upgrading to 2.5.0 for example, Terragrunt will update the provider.tf in all my directories next time I run terragrunt apply.

But let's say one of my directories is affected by a bug so I can't upgrade to 2.3.1. In that case I'd like to remove the Terragrunt signature from the file, downgrade to 2.3.1, and then Terragrunt won't replace the provider.tf file next time I run a command.

When the bug is fixed (maybe in 2.5.1) I'd be happy to remove the file and let Terragrunt generate it again.

[brikis98]

I gotcha, thanks for the explanation. Would you be up for a PR to add a new if_exists setting to handle this use case?

[anlutro]

Sure thing, I can probably spend some time on it this week.

Any ideas on what the new setting should be called? Something like soft_overwrite comes to mind but I'm really not sure.

[brikis98]

Thanks! I'm terrible at naming things. I'd probably pick something super verbose like overwrite_terragrunt_else_ignore, but feel free to toss out (hopefully better) ideas!

[artemsablin]

Would this help?

[askainet]

Would this help?

It helps indeed!

I'm using it to ignore the EKS managed tags from my VPC component in a provider-aws_override.tf file:

provider "aws" {
  ignore_tags {
    key_prefixes = ["kubernetes.io/cluster/"]
  }
}

[gitPlatformTests]

Was this implemented or about to be? I find it useful and the override feature of tf is not enough